add trybuild tests to routing codegen (#1677)

actix-web-codegen/tests/trybuild/simple.rs

@@ -0,0 +1,15 @@
+use actix_web::*;
+
+#[get("/config")]
+async fn config() -> impl Responder {
+    HttpResponse::Ok()
+}
+
+#[actix_web::main]
+async fn main() {
+    let srv = test::start(|| App::new().service(config));
+
+    let request = srv.get("/config");
+    let response = request.send().await.unwrap();
+    assert!(response.status().is_success());
+}